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1. re-create the FB app.. the settings like on screenshoot :
2. Change the Jomsocial template to default instead weareonthelist template
and after that I login via FBC and everything is working fine..what I suggest is.. please you use default jomsocial setting and follow the FB app setting like mine.
I have done the steps you mentioned without no effect.
As I told you in one post, I noticed that there was an app id in the facebook login pop-up that didn't appear in our platform.
I have searched this ID in Google and finally found the solution to my problem. Apparently there is a javascript conflict with SH404SEF social buttons plugin. I have disabled this plugin and everything works perfect again.
Here you are the link to the thread of the SH404SEF support forum. It can be helpful for other users...